1. Field of the Invention
The present invention relates to a laminated SOI (Silicon On Insulator) substrate for use in forming a semiconductor device and a producing method thereof, and more particularly, to a laminated SOI substrate in which the adverse influence, on a device, of defects in the substrate is reduced, and a producing method thereof.
2. Description of the Related Art
As a method for producing a super thin film SOI substrate by a lamination technique, there is known a smart-cut process utilizing a phenomenon that a semiconductor substrate is cleaved through voids formed by charging a large amount of hydrogen (Proceedings 1996 IEEE International SOI conference, p152). FIGS. 1A to 1E are sectional views sequentially showing a producing method of the SOI substrate by the conventional smart-cut process.
In the producing method of the SOI substrate according to the conventional smart-cut process, silicon dioxide film 22 which is an insulation is first formed on a single crystal silicon substrate 21 as shown in FIG. 1A. A surface area of the single crystal silicon substrate 21 ultimately will be a device forming area. On the surface area, oxygen deposition or crystal defect region 28 such as nucleus of the oxygen deposition which is called a grown-in defect as a general term exists.
Next, as shown in FIG. 1B, hydrogen ion is ion implanted from a surface of the silicon dioxide film 22 in a dose amount of about 10.sup.16 to 10.sup.17 (atoms/cm.sup.2). As a result, a hydrogen implanted region 23 is formed in the single crystal silicon substrate 21.
Then, as shown in FIG. 1C, a surface of the silicon dioxide film 22 and a surface of another single crystal silicon substrate 25 are laminated at room temperature, and are subjected to a thermal treatment at 400 to 500.degree. C., thereby forming voids 24 in the hydrogen implanted region 23.
At that time, as shown in FIG. 1D, the single crystal silicon substrate 21 is cleaved through the voids 24 formed in the hydrogen implanted region 23.
Next, a thermal treatment at about 1,000.degree. C. or higher is carried out for several hours to strongly adhere the laminated surfaces of the silicon dioxide film 22 and the single crystal silicon substrate 25. Then, a surface of the cleaved single crystal silicon substrate 21 is polished to form a mirror surface to complete the SOI substrate.
Then, the SOI substrate produced in this marier is advanced to a device forming step.
However, in the laminated SOI substrate produced by the above-described conventional method, there are problems that particles are generated in the device produced using the SOI substrate, or bonding leakage, element separation characteristic and tolerance voltage of gate insulation film are deteriorated.